In an automatic transmission which is applied to a vehicle, a gear shift control apparatus controls hydraulic pressure by controlling a plurality of solenoid valves in accordance with a traveling speed of the vehicle, an opening degree of a throttle valve, and various detection conditions, such that a shift gear at a target gear shift stage is operated, and as a result, a gear shift operation is automatically performed.
That is, when a driver changes a range of the gear shift lever to a desired gear shift stage, a port change of a manual valve is performed, and hydraulic pressure supplied from an oil pump is selectively applied to various operational elements of a shift gear mechanism in accordance with a duty control of the solenoid valve, such that the gear shift operation is performed.
Meanwhile, when high torque is applied to a specific clutch, pressure corresponding to the high torque needs to be applied to the clutch, but in the related art, a slip may occur in the clutch due to a limitation of pressure that can be controlled by the solenoid valve, and the transmission may break down due to the slip.